Scala Language Currying Currying


Let's define a function of 2 arguments:

def add: (Int, Int) => Int = (x,y) => x + y
val three = add(1,2) 

Currying add transforms it into a function that takes one Int and returns a function (from one Int to an Int)

val addCurried: (Int) => (Int => Int) = add2.curried
//               ^~~ take *one* Int
//                        ^~~~ return a *function* from Int to Int

val add1: Int => Int = addCurried(1)
val three: Int = add1(2)
val allInOneGo: Int = addCurried(1)(2)

You can apply this concept to any function that takes multiple arguments. Currying a function that takes multiple arguments, transforms it into a series of applications of functions that take one argument:

def add3: (Int, Int, Int) => Int = (a,b,c) => a + b + c + d
def add3Curr: Int => (Int => (Int => Int)) = add3.curried

val x = add3Curr(1)(2)(42)